1. Field of the Invention
The present invention relates to a process of producing an opacified molded product composed mainly of a polypropylene resin. More particularly, it relates to a process for producing a stretched and molded product having a feeling of opacity or pearly quality imparted by stretching a molded product of a composition comprising a specified amount of a cyclopentadiene petroleum resin and/or its hydrogenated product blended with a crystalline polypropylene.
2. Description of the Prior Art:
Molded products having a feeling of pearl or opacity generally have been used as containers and also for general packaging materials, decorative materials, synthetic paper, transcription printing paper or the like, e.g., in the form of a uniaxially or biaxially stretched film. Further, they have been widely used for packing materials, weaving yarns, etc. in the form of a tape, a ribbon or a filament.
Examples of methods of producing a molded product having a feeling of opacity or pearly quality known in the art include (1) a method wherein a brightening agent, such as white pigment, extender pigment or pearl essence, is added, (2) a method wherein a foaming agent is added during molding to form a number of cells, (3) a method as described in Japanese Patent Publication No. 24532/1988 and Japanese Patent Laid-Open No. 117043/1988 wherein a large amount of an inorganic filler is added and the mixture is stretched to form voids, and (4) a method wherein a molded product is treated with a solvent, chemicals or the like to dull the molded product.
The above-described methods have the following drawbacks. Specifically, in method (1), it is necessary to use proper pigments respectively for imparting the feeling of opacity or pearly quality, and further the pearl essence is very expensive. Moreover, it is necessary to use a mixing method and apparatus to which particular consideration has been given for the purpose of improving the dispersibility of the above pigments. Method (2) has drawbacks such as the necessity to select the foaming agent to be used depending upon the molding conditions and the applications of the molded product, and the difficulty of forming uniform and fine cells when a thin membrane such as a film is formed. In method (3), addition of a large amount of an inorganic filler brings about many troubles during production of the molded material, such as a remarkable lowering of flowability during extrusion, occurrence of clogging of a screen pack, high susceptibility to moisture absorption, foaming and poor dispersion attributable to the use of the inorganic filler, and the necessity of a long period of time for purging resins in the molding machine. Further, in this method, only molded products having lowered glossiness and a roughened or rough surface are prepared. In method (4), the treatment is conducted in a post-treatment step, and it is necessary to remove the solvent and chemicals, which is disadvantageous from the viewpoint of apparatus and cost. Further, in this method, although a molded product having a feeling of dullness can be prepared, no molded product having a pearly feeling, can be prepared.